1. Field of the Invention
The present invention relates to photoetch plates and more particularly to a photoetch plate hinge for securely positioning two photoetch plates about a sheet of material.
2. Description of the Prior Art
Photoetch plates are used to create intricate metal structures. Such metal structures include lead frames which are commonly used to electrically connect integrated circuit chips to discreet electrical componentry. The creation of such structures via photoetching requires the disposition of a metal sheet between two photographic plates. The plates are typically glass onto which a desired design or mask pattern has been recorded. The metal sheet has a radiation sensitive coating of "resolve" on the side to be etched. Upon exposure to radiation, the resolve coating undergoes a molecular change.
The metal sheet and the photographic plates are placed in a vacuum device and a radiation source such as a high intensity ultraviolet light is passed about the sandwiched structure. The vacuum device is used to compress the plates against the metal sheet to ensure high resolution irradiation. The sheet is then removed from the photo plate sandwich and processed further to create the lead frames.
Time is consumed in the proper placement and removal of the sheet from between the photo plates. Proper registration or alignment of the photo plates and the sheet is critical to prevent waste. Improper registration of any plate or sheet by greater than two ten thousandths (0.0002) of an inch results in one side of the metal sheet being irradiated in improper alignment with the other side when both sides of the plate are irradiated. This results in low quality or waste sheets.
To speed up the placement of the metal sheet between the photo plates, and to ensure proper registration of the plates and the sheet, the photo plates are hinged together. Use of hinged photoetch plates is known in the prior art. The prior art discloses the use of a flexible plastic hinge secured to one end of each photo plate. A glass protective shield is flexibly secured to the hinge. The sheet material is disposed between the two plates by lifting the top plate from the bottom plate in a vertical arc-like manner and inserting the sheet. The plastic hinge functions as a fulcrum. Once the sheet is inserted between the plates the top plate is lowered over the sheet. The prior art also utilizes a burr channel. A burr channel is a small cavity created in one of the plates to prevent burrs on the edge of the metal sheet from cracking the photo plates when such are placed in a vacuum. Furthermore, the burr channel is necessary to allow excess resolve or resolve that has beaded up on the edge of the metal from interfering with the etching process. There are numerous disadvantages with the prior art.
One disadvantage of the prior art is its use of a plastic hinge. Plastic hinges do not have the same coefficient of expansion as glass photoetch plates resulting in a loss of registration between the plates and/or the sheet when high temperature radiation lamps are used to irradiate the sheet.
Another disadvantage of the prior art is its use of a glass protective shield over the plastic hinge to prevent loss of registration due to hinge deformation caused by the vacuum pressure during irradiation. Use of such a glass protective plate is expensive and contributes to photoetch processing costs.
Another disadvantage of the prior art is that glue used to adhere the plastic hinge to the plates migrates into the burr channel and contacts the metal sheet. When the metal sheet is removed, the glue smears on the sheet or the photoetch plates fouling the plates and/or destroying the irradiated surface of the sheet.
A further disadvantage of the prior art is that once glue contacts the metal sheet or the plates it induces uneven stress on the plates resulting in cracking or breakage of the photo plates when such are subjected to vacuum pressure.
Another disadvantage of the prior art is that the photo plates are not totally accessible for cleaning. Removal of surface impurities or glue from the photo plates is impossible in the portion of the plate closest to the hinge. This prevents the removal of undesirable foreign particulate matter from the plates thereby reducing the effective usable life of the plates.